As to a conventional structure of a hybrid vehicle, for example Japanese Patent Laying-Open No. 2001-138753 (Patent Document 1) discloses a vehicle lower body structure of a hybrid vehicle having an object of lowering the floor while reducing the length in the longitudinal direction of the vehicle. In the hybrid vehicle disclosed in Patent Document 1, a battery case storing a battery is arranged below a seat in the vehicle room. An exhaust pipe attached to an exhaust manifold of an engine extends below a floor panel toward an exhaust port situated at the rear of the vehicle. The exhaust pipe extends in a position not overlapping with the battery when the vehicle is seen two-dimensionally.
Japanese Patent Laying-Open No. 2003-326980 (Patent Document 2) discloses a loading structure for an exhaust pipe, which has an object of suppressing a local temperature increase of a battery caused by heat of an exhaust pipe. Similarly to the hybrid vehicle disclosed in Patent Document 1, also in Patent Document 2, the battery is arranged so that it is not positioned immediately above the exhaust pipe.
Japanese Patent Laying-Open No. 2001-18664 (Patent Document 3) discloses an air-intaking and exhausting apparatus in an air cooling system having an object of efficiently cooling a power drive unit and a down converter without using an air conditioning apparatus in the vehicle. Japanese Patent Laying-Open No. 2000-351328 (Patent Document 4) discloses a battery mounting structure for an electric vehicle having an object of mounting a battery on one side below a vehicle floor without impairing support stability.
A battery pack mounted on a hybrid vehicle is classified by the direction of the flow of cooling air into a side-flow type wherein the cooling air is caused to flow in the horizontal direction to cool the secondary battery, and an up-flow type or a down-flow type wherein the cooling air is caused to flow in the vertical direction to cool the secondary battery. With the side-flow type, an intake chamber supplying cooling air toward the secondary battery and an exhaust chamber exhausting the cooling air from the secondary battery are arranged on opposite sides of the secondary battery. However, in this case, since there is no chamber below the secondary battery as in the up-flow or down-flow type, the battery pack is greatly affected by heat from under the floor panel when the battery pack is arranged on the floor panel of the vehicle. This may impair the efficiency of cooling the secondary battery.
On the other hand, in the hybrid vehicle disclosed in Patent Document 1, the exhaust pipe is arranged so that it does not overlap with the battery when seen two-dimensionally. However, the exhaust pipe must be detoured around the battery case, and therefore the pipe is greatly bent along its route. When the exhaust pipe is excessively bent in such a manner, exhaust efficiency may be reduced and the engine performance may be impaired.